


For Science!

by Lhugy_for_short



Category: Final Fantasy XV
Genre: Blood Kink, Demon Gunk Kink, Demonic!Ardyn, Dubious Consent, M/M, Power Play, Power bottom!Verstael, Rough Sex, Touch-Starved
Language: English
Status: Completed
Published: 2019-12-25
Updated: 2019-12-25
Packaged: 2021-02-26 04:54:00
Rating: Explicit
Warnings: Graphic Depictions Of Violence, Rape/Non-Con
Chapters: 1
Words: 4,394
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/21957703
Author URL: https://archiveofourown.org/users/Lhugy_for_short/pseuds/Lhugy_for_short
Summary: At long last, Verstael Besithia has the demon Adagium in custody. Years of research, of fruitless experiments and failures, have led to this momentous opportunity. And he's willing to go to any lengths in the name of science.
Relationships: Verstael Besithia/Ardyn Izunia
Comments: 6
Kudos: 56
Collections: Final Fantasy XV NSFW Secret Santa 2019





	For Science!

**Author's Note:**

> For the FFXV Naughty Secret Santa event! My giftee was Ryuuza (@ryuuzarotic on Twitter), who had lots of delicious requests! The ones I picked were Ardyn/Verstael + blood play and demon fucking lol. I really hope you like how it turned out, darling! 
> 
> Happy Smutmas, everyone *heart*

_ Adagium.  _

He dragged his fingertips down the thin pane of glass that separated him from the creature. No, the  _ man _ , he corrected himself, for there was no mistaking the likeness. Two arms, two legs, the broken, beaten body of a mortal, and yet…. Adagium was not entirely human. That much was certain. They had all seen the monstrous power he’d unleashed at Angelguard. 

_ Demonic, dark energy. The legendary Bane of Lucis.  _

Against the glass, Verstael scoffed. Years of research had led to this very moment, to the acquisition of a weapon that could at last turn the tides of war in his Emperor’s favor. Centuries of riddles, trails of clues that only a genius like himself could have ever unraveled. He, the same scientist who had learned how to subdue literal gods, had also become the first to uncover the secrets of the ancient Solheim curse. 

Yet his efforts left him decidedly disappointed. Adagium was...weak. Sickly, even, drained near to death by a power he could not control.  _ This _ was the monster Lucis had guarded for two millenia? At least Ifrit, even frozen on ice in the laboratory basement, struck fear into those who set eyes on him. 

Adagium? He inspired in Verstael nothing but pity. 

Above him, a speaker crackled to life in the dark mire of his thoughts. “ _ S-ir. The sp-ecimen appea-rs to be gaining conci-ousness.”  _

Finally. He switched a light on in the containment cell, a stark-white room containing a cot, a single stool (upon which Adagium himself now sat, bound), and a small aluminum desk that doubled as a restraining table. Just in case. 

“Prepare the hoses. I’m going in.” 

“ _ Sir, a-re you cert-ain that’s wi-- _ ”

Verstael shut off the speaker with the flip of a switch. The comms shifted from the interphone system to a small bud already fitted into his right ear. “Question me again, Elena, and I’ll have you demoted to infantry within the week. Are we clear?” 

“ _...Y-yes, Doctor Besithia. _ ”

“Very well. Read me the vitals report.” It was a superfluous request, of course. He could see all of the data they were monitoring right on his tablet screen, from Adagium’s heart rate to his brain activity, recorded in real time by the wires and machines connected to his half-naked body. But he did so like to keep his assistants on their toes. Idle hands, after all, did the work of the devil. 

“ _ Sir. Heart rate is 115 bpm. Internal temperature is high, nearly 38 degrees. Subject is showing signs of stress, mainly in the amygdala, possibly caused by nightmares.”  _

Again, Verstael found himself scoffing as he unlocked the heavy door to Adagium’s cell. “Nightmares? What in Eos could frighten a bloody demon, for fuck’s sake.” 

Unsurprisingly, his assistant didn’t have an answer for that. The comm fell silent - the voice there waiting dutifully for further instruction - so Verstael turned his attention elsewhere. Namely, to the body still bound and bowed in the center of the room. 

Though still noticeably emaciated, Adagium was cleaner than the last time they’d met, back in the caves of Angelguard where he’d been chained for two thousand years. Amazing what a little soap and water could do for the smell. His hair, however, could use some work in Verstael’s opinion. And the beard. Perhaps they could work on grooming after they’d come to a deal on Niflheim’s behalf. 

“Adagium,” he started, enunciating each syllable on the off chance that the demon didn’t speak the common tongue. “Are you awake, Adagium?” 

There was a sound, more rasp than answer, on a throat weak with disuse. Though the monster did not lift his head, Verstael noticed the way tired, golden eyes slid open to look at nothing in particular near his feet. 

He frowned. “You’re going to have to speak up. I’ve already gone to the trouble of rescuing you from that infernal rock, the least you can do in return is acknowledge my questions.” 

For a long moment, there was silence. Verstael wondered if perhaps Adagium had slipped back into unconsciousness, or if he didn’t understand his words after all. But then, slowly, parched lips parted, and Adagium spoke in a painfully forced voice. 

“My name. Is Ardyn. Not...Adagium.”

“Now we’re getting somewhere.” For his efforts, Verstael was considerate enough to grab a clear plastic bottle from the table, and hold the water open in front of the demon’s mouth. “Thank you. Cooperation is rewarded here, you see.” 

“Where,” Adagium -  _ Ardyn _ \- began once he’d drained half of the bottle in one breath. “Where is here?” 

“You are in a laboratory in Gralea, the capital of the Niflheim Empire. I am the chief scientist, Verstael Besithia, and you are currently in my custody.” He paused, waiting for the unfamiliar words to finish rattling around in Ardyn’s ears. “All you need to know is that you answer to me. There are so many things I hope to learn from you….” 

He couldn’t resist touching him. Just a stroke of fingers over the curve of a shoulder, fleeting and yet the touch left him more curious than before. So many years of research, so many factors  _ unknown _ . To have the legendary monster so close now, it would be cruel to deny himself the chance. As he walked around Ardyn’s slumped form, he trailed his fingers over harsh bruises, the muscles beneath the bare skin of his upper back. Up to his neck where wine-red hair fell in unruly curls. And he smirked. “You are not at all what I expected.” 

If Ardyn noticed his ministrations, he gave no sign. “I care not what you expected. You called me a monster at Angelguard, and you were right. I should not be alive. I ask you to kill me.” 

“ _ Tsk _ . How would that be of any benefit to me? You’re useless to me dead.” 

“Kill me,” Ardyn repeated, more forceful this time as golden eyes flashed up to meet his own inquisitive blue. “Kill me, or I will destroy you and every living soul in this building. I am a  _ murderer _ .” 

_ Ah,  _ now this was more like it. Verstael loved a challenge. He thrived off of taking control, of bending resistance to his will. He much preferred this version of Adagium to the despondent wastrel they’d first dragged into the lab.  _ This  _ was a problem he could work with. 

“I will do no such thing, and neither will you. I did not risk my valuable equipment to free you from your shackles, only to have you die on my watch here. No, you're of far more use to me alive." 

Ardyn's response was a cough, wet and deep in his throat. A second time as his body lurched forward, and he fell to his knees on the cold floor, snapping wires left and right on the way down. " _ Curse…you…,"  _ he rasped, though to whom it was unclear. Behind his back, his hands strained against their bonds. " _ I do not want this!"  _

Verstael was torn. On one hand, as a man of science he was loathe to interfere with a specimen in its natural state. Each word out of Adagium's mouth offered more insight into what already amounted to a lifetime of research, and then some. 

On the other hand, he appeared to be in genuine pain. Certainly, Verstael didn't consider himself a philanthropist. Yet to watch this poor, broken man writhe on the floor, black ooze dribbling from his lips as he cursed some unseen tormentor - it was cruel even for him. 

"Come now. Get ahold of yourself." Then, tapping the comm unit in his right ear, he added, "Bring a towel. And more water, with ice." 

The clipped  _ yes, sir!  _ he received in response was nearly drowned out by the pained sobs of the man on the floor. Verstael lowered himself, reaching out to lay a soothing hand on Adagium's shoulder. "There, there. It will pass." 

The demon muttered something. His lips were stained black now, more of the dark ooze spilling from his lips and even his eyes now in place of what may have been tears. When Verstael rolled him onto his back on the floor, there was no resistance. Only a hazy look in the golden rings of his eyes as he gazed up at the ceiling high above. 

"Please," he whispered. There was almost a tenderness to the way Verstael brushed sweat-matted hair from his forehead, his sullen cheeks. "Release me from this." 

"No." 

Lips stretched in a grimace, Ardyn's teeth ground together on the verge of a scream. " _ I'm begging you!"  _

Distantly, the sound of the door opening. Versteal glanced over his shoulder to see his assistant hovering against the far wall, towel gripped between white-knuckled fists. And he sneered. "There is no need to be afraid," he said, as much to her as to Adagium across his lap. "Fear itself is weakness." 

Hesitantly, the woman took a few steps forward, close enough to hand over the towel and bottle of water, but no further. Verstael thanked her with a dismissive wave. 

"Your service is no longer required today. That will be all." 

"But, sir--"

"Out!" 

He had warned her, hadn't he? What a shame to see such potential wasted on the battlefield, but he had no use for assistants who couldn't follow orders. In the morning, he would fill out the paperwork for a new - less opinionated - intern. As for tonight…

Adagium's unfocused eyes watched him fold the towel, bring it in close to dab at the black ooze staining his mouth. Almost gentle, almost loving. Yet Verstael did nothing without a degree of scientific coldness, without first calculating every equation to weigh in his favor. And so, after wiping the last of the mess from Ardyn’s chin, he made sure to fold the towel and slip it discreetly into his lab coat pocket. 

“There, all better now. Can you stand?” Ardyn said nothing, but neither did he struggle when Verstael moved to help him up. He swayed on his feet, unbalanced, and his fingers clenched to fists at his back where his wrists remained bound. Curious, Verstael thought, that he hadn’t yet begged to be freed from them. Was he so frightened of his own power that he preferred to be restrained? Or was he merely biding his time, waiting for his full strength - the strength Verstael had witnessed him unleash back on Angelguard - to return? 

Somehow, he found the latter an infinitely more thrilling prospect. 

“Now, I believe we’ve established a level of rapport between us, have we not?” he smiled. The various wires and electrodes that had been connected to Ardyn’s body littered the floor, but Verstael toed them aside, a show of trust. “I help you, you help me. I help you again…. Well, you get the idea.”

“Do as you please. I care not.”

That sharp grin grew wider. “Oh? But you haven’t even heard what I want from you. Are you so eager to relinquish control?” 

“I am  _ tired _ ,” Ardyn, growling, replied. “And you insist on keeping me alive for some godsforsaken purpose, so I am asking you to  _ get the hell on with it _ .” 

_ Yes,  _ Verstael thought,  _ bare your fangs. Show me the rage that lives within you _ . Aloud, he said simply, “Allow me to examine your wounds.” 

He remembered very clearly the scene within Adagium’s prison chamber. The chains, thick and ancient, carved out of the very stone; the hooks which tore open the flesh of Ardyn’s back, his arms, suspending him from the ceiling above; the blood, so dark it appeared black as night, running down his body in an endless, merciless torture. 

Verstael had seen the macabre display with his own two eyes, and yet now, as he pressed his fingers to the skin above Ardyn’s ribcage, he found it impossibly whole. No cuts, not so much as a scar where the hooks had dug into his flesh for centuries.  _ Fascinating _ . He moved to Ardyn’s back, ran his palms over the muscles there, felt them shudder and tense under his touch. 

“Subject displays signs of rapid regeneration,” he observed aloud, aware that the cell’s AV equipment would record his notes for later. “Possible influence from his mutated genetic structure. Implications for Phoenix Project? Further research required.”

“Who are you talking to?”

“No one. Myself.” From inside his robes, Verstael produced a scalpel, the steel blade small but sharp as he pressed it to Ardyn’s shoulder blade. “Tell me, does this hurt?” 

Just a nick, so fast Ardyn didn’t have time to flinch away. It left a shallow cut behind in its wake. As he released a hiss at the sting of it, black droplets of blood swelled to the surface, pooled together, then sank out of sight again as the wound sealed up. 

“If you wish to hurt me, you’ll have to try harder than that.” 

Excitement filled him at the challenge - and, admittedly, at the rough edge to Ardyn’s voice. The  _ darkness _ there, so raw he could almost taste it on his own lips. Subconsciously, his tongue flicked out in search of it. 

“Subject’s body appears to heal almost instantaneously. He  _ claims _ to feel no pain, though such data is objective and unreliable. Further testing required.” Verstael rounded on Ardyn, icy blue eyes fixed on smouldering yellow. The tension between them was palpable, particularly now that Ardyn, standing at full height, towered at least a head taller. Like a battle for dominance, both were refusing to back down. 

The scalpel pressed to the center of Ardyn’s bare chest. Drew a line of fire down his sternum, just enough to force a grimace to his face, before Verstael was moving on. A deeper cut below his ribcage allowed a trickle of black blood to skate down his side. This Verstael caught with his thumb, smearing it in a shadowy arc across starkly pale skin. With nowhere to escape, it lingered there, evidence of the fine lines between science and pleasure that had already begun to blur. 

For Verstael, the difference in the two was only a matter of time. 

He let his eyes drink in the sight of Ardyn’s body, down, down to where the flat of the scalpel tapped impatiently against loose cloth. The grey sweatpants he wore were standard military issue, the only clothes in his size they could find in the lab. But now. Verstael smirked, they were in his way. 

Wordlessly, he tugged the end of the cord that held them in place, releasing the knot there. Ardyn’s expression strained - not a ‘no,’ exactly, but decidedly wary - as his pants were slid down over his hips, his thighs, finally into a pool on the floor at his feet. Until he stood naked, hands still bound behind him, and seemingly at Verstael’s mercy. 

“How long has it been?” The question dripped from Verstael’s lips like sweet poison, both an offer and a trap. “How long since you felt the touch of another? All those long centuries locked away…. Did you not long for it?” 

“You know nothing of what I’ve suffered.” 

Nodding, he dropped the scalpel to the space between Ardyn’s thighs. Ghosted the sharp edge of the blade up his leg, higher and higher to dance around the base of his cock. Which, much to his delight, twitched in response. “I do not. Nor can I begin to imagine the toll all those years of isolation must have taken on your mind. The loneliness, the emptiness. It surely left you quite…twisted." 

A snarling groan. Verstael's scalpel carved a dark line into tender flesh, and in turn Ardyn yanked with real intent at his restraints. The bonds held as drops of black, quivering blood dripped to the linoleum tiles below. 

"My, but you are sensitive. Just look at how eagerly your body soaks up all this attention. How it thirsts for more." Ardyn might have said something, but Verstael chose that moment to replace his scalpel with his own hand, surrounding the thick flesh with warmth instead. He found praise in the slurred curses that fell from Ardyn's mouth, encouragement even. He tightened his fist, stroked the length of Ardyn's cock as the wounds -  _ his own work -  _ closed again inch by inch. Dark blood helped to slick heated skin. Had Verstael's fingers flying faster, hotter as Ardyn's tall frame buckled under the onslaught. 

"G…gods… _ please _ ." 

"You still pray to them?" His tone was mocking, cruel. "After everything you've suffered, you continue to look to your tormentors for release? Fool. I am the one you should be begging.  _ I  _ am the one who will see your every desire made real." 

Panting breaths. Ardyn shuddered, gasped for air, his cock now thick and throbbing with two thousand years of unsated need. "W…why?" he asked. 

"Why, for science, of course." And he meant it. When he tossed the scalpel aside and crushed his mouth to Ardyn's, it was for science. When he shoved him back onto the stool and dropped to his own knees between Ardyn’s thighs, it was for science. When he licked his tongue up the heated underside of Ardyn's shaft, noting the taste, the texture, the weight of it in his mouth, that, too, was - at least in part - for science. 

No one could ever claim he didn’t enjoy his work. 

Natural curiosity drove him on. How much could Ardyn actually handle? How long could he maintain the illusion of control under such...enthusiastic ministrations? Verstael sealed his lips tight around the base of hard flesh, and felt as well as  _ heard _ Ardyn’s composure crack a little more.  _ Not much longer at all _ , he hypothesized. It was almost a shame the demon was still bound; Verstael might have liked to know what those fingers felt like raking through his hair on climax. 

Yet despite the breathy groans that spilled endlessly from Ardyn’s throat, he seemed to be no closer to finishing even several minutes later. Verstael’s jaw was beginning to ache with effort. He tried adjusting the factors - moving faster, then slower; adding a hint of teeth when he pulled back to suckle on the head - but all produced the same results. It was becoming clear that Ardyn had a better grip on control than he’d previously thought.

He released the cock from his mouth and, breathless, turned his attention to his own extraneous clothing. “No need to hold back,” he panted. “Not on my account. I  _ want _ to see you unleashed.” 

Heated yellow eyes watched first his lab coat, then his neck tie flutter to the floor. “No. You don’t. I am a--” 

“A monster? A  _ demon _ ?” Stepping out of his grey slacks, Verstael stood before Ardyn wearing nothing but a smirk. Unafraid, unmoved. “ _ Adagium _ , Devourer of Souls, Bane of the Lucian Kings. I’ve read the scripture, and I have long desired to see your work with my own eyes.” 

“N-no….” Ardyn trembled, skin flushed with emotion and the strain of fighting his need. "You don't know. You weren't there…." 

"Show me, then." 

"Stop this!"

Verstael was kissing him again, more forceful this time and with no warning. The momentum of it was enough to throw him off balance, to send the stool clattering to the ground and the two of them close after it. Ardyn's back hit first. He grunted in pain as his bound hands were trapped under their combined weight. But Verstael had a solution for that, as well. 

A flick of his thumb unlocked the metal cuffs around each of Ardyn's wrists. They slid open, and he tossed them far across the room. There was a tense moment, one in which Ardyn's hands clenched into fists, reared back as if to strike. Then his yellow eyes hazed over - with sadness, with regret - and he curled his fingers around the back of Verstael's neck instead, dragging him down into a bitter kiss. 

The experiment resumed. Hands flew over touch-starved flesh, teeth marked their claims in trails of dark bruises down bared throats. Verstael kicked over the table in his urgency to get the medical kit there, and while Ardyn growled hungrily around the fingers in his mouth, he sought out the bottle of lotion stored in the box.

Ardyn didn't offer to touch him, and neither did Verstael ask. He prepped himself without ceremony, wetting his already slick fingers and working himself open with calculated efficiency. The growl when he sat back against his cock - a wholly inhuman sound, thick with feral need - was all the encouragement Verstael needed. He hummed as the head of Ardyn's dick stretched past tight muscles. Bit down against the pain, and focused on how his body adjusted to accommodate its girth. One by one, he catalogued each sensation of pleasure - the ripples, the bursts, the slow undulations as he was filled from the inside.

_ Fucking a monster. _ Verstael would be lying if he said the prospect hadn’t always intrigued him. Though trapped within the weak body of a man, he could sense the power Adagium still possessed even now. Could feel the darkness like a hunger beneath the surface of Ardyn’s skin, and throbbing inside him where they joined together. When Ardyn growled, the darkness growled with him. When he dug his nails into the flesh of Verstael’s hips, hard enough to draw blood, the demon within gained that much more control. 

“ _ Yes _ .” He kept his voice low, barely a whisper against the shell of Ardyn’s ear. “Why keep fighting? Let him out to play.” A controlled roll of his hips had the cock inside of him slamming in deeper, and the shadows that gathered in unfocused yellow eyes darkened. “Give me  _ Adagium _ .”

He should have seen it coming, the hand that struck out for his neck. But Ardyn -  _ no, not Ardyn, not anymore _ \- was far too fast. Fingers squeezed around the base of his throat, so tight he couldn’t cry out in his surprise. All that left his sex-bruised lips was a whine, a half-choked name as his lungs began to burn for air. 

The demon Adagium did not speak. His eyes, swallowed up now in shadow, leaked once more at the corners to run in dark streaks down his face. As he pushed himself off the ground, Verstael was lifted with him, bare thighs shaking and fingers clawing at the grip around his neck. 

_ Domination. Fear.  _ This was indeed the power he’d been seeking. Raw and unchained, the true monster free at last. Despite, or perhaps enhanced by, the panic coursing through his veins, Verstael trembled with ecstasy. Could Adagium see it in his eyes? The lust, the  _ need  _ to feel more of that power? Did he want it, too? 

It would have been so easy for the demon to kill him then. Yet, rather than tightening, the cruel fingers around his throat instead cast Verstael to the floor. He landed on his side, and gasped at the first breath of icy cold air to fill his chest. Several more breaths and then he was laughing, the sound distorted around the strain in his voice. 

Then Adagium was on him again, pressing Verstael’s hips flush to the floor as he forced his way back into tight, slick heat. Taking him with almost bestial brutality, fingers digging like claws into the skin of his thighs, his back, his scalp. Bruising him, fucking him.  _ Claiming _ him both inside and out. And Verstael, half-mad with the intensity of it, groaned for more.

But the demon, much like the man, still had limits. Teeth sunk into Verstael’s shoulder as Adagium released a tormented howl. His frame shuddered once, twice, gave a final lurch forward before filling the body beneath him with hot seed. The throes of climax gripped him for a long, desperate moment, until the air began to cool and the shadows surrounding him lightened. Yellow eyes, still sad but deeply sated now, slid closed as softly as a prayer. 

From over his shoulder, Verstael watched Adagium slip away. Not gone, he knew, merely retreating into the recesses of the mind he shared with Ardyn. Who would have thought that demons could need a refractory period? Two thousand years in chains and one good fuck was enough to silence him again? Verstael smirked. Unexpected as it was, he considered it a fascinating - and practical - discovery. 

Getting to his own feet, however, was more of a challenge than he’d anticipated. Careful of the cuts on his thighs and the dark liquid leaking down between them, he limped past Ardyn’s docile form to snatch his lab coat off of the floor. “Elena. Elena!” he hissed, readjusting the comm in his ear. “Blast it, girl, tell me you haven’t left yet.” 

There was a pause, and then: “... _ No, sir. I’m in the research lab. I...was worried about you.”  _

“Nevermind that. Bring a fresh medical kit to the holding cell. And another bloody towel!” 

He tugged his coat tight around him, willing his legs to stop buckling beneath his own weight. If it weren’t for the way his knees were threatening to give out from under him, he might have gotten the supplies himself, spare the trouble of letting his assistant see him like this. Or Ardyn, for that matter, who sat rocking gently on his heels, as weak and harmless as--

The cell door slid open in a rush. His assistant stood frozen, eyes already going wide as the shadows dragged her bodily into the room. Darkness surrounded her, clamped down before she ever had a chance to scream. In the blink of an eye, she was consumed,  _ devoured _ by the shadows. All that was left to clatter to the floor was the medical kit she’d been clutching in her hands. The rest vanished along with the inky blackness that was absorbed back into Ardyn’s body where he still sat on the floor. 

_ He’d never even lifted a finger _ .

A long silence passed, broken only when Verstael, frowning, clicked his tongue. “I’ll ask you not to eat any more of my assistants, please. They don’t exactly grow on trees, you know.” No response. “If it’s souls you’re after, I suppose we can come to an...arrangement, of sorts. But remember.” 

Yellow eyes peered open again as he rounded on Ardyn. Snatched up his stubbled jaw in his fingers, and held his gaze with a deliciously wicked look of his own. 

“Nothing for free.” 


End file.
